Scott,

Personally I don't know of any drawbacks. We use .013 and .020 diameter vias
also.
We also go one step farther (which it may seem like overkill). Before we
apply the LPI
we apply the standard PC-401 over the vias only. Once that has cured, we
apply the
LPI over both sides of the board. We do this to insure that all of the vias
are plugged and no air is
drawn through when the vacuum is applied during testing.

I have seen some thinning of the LPI when it does draw into the hole, but it
really isn't
enough to cause problems. I think this will vary depending on what brand of
LPI is used.

One advantage to tenting the vias is that you can drop the power and ground
vias right next
(tangent) to the power and ground pins of the ICs. We have seen a tremendous
reduction in noise
when we started to do this. With the via being tented, the soldermask acts
as a dam and
prevents the solder from being drawn into the hole.

This will definitely take care of some solder bridging issues.

Sincerely,

John Bauer
IDEO Product Development



-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]]On Behalf Of Scott
Buscomb
Sent: Friday, May 15, 1998 9:29 AM
To: [log in to unmask]
Subject: [DC] Soldermask over Vias


What are the drawbacks to tenting vias? I am planning on tenting vias
using LPI both sides on SMOBC. The vias are .013 and .020. I realize the
LPI is pulled into the holes causing a thinning of the mask.
I am trying to prevent solder bridging during reflow and wave soldering.

Any comments would be appreciated.
TIA,
Scott Buscomb

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